At 8 mos, she's probably ready for a bit longer A time - my guess is that's why you've gotten a 40 min nap. You may want to try extending her A times just by 15 min and see if that helps any. She also then could probably cut out her cat nap entirely. At first, you may need to move bedtime 15 min earlier til her A times get sorted out, but she should be able to go close to 3 hrs of A time, then with 2 naps.
HTH
michelle